The present invention relates to a glass keyboard and to a method for producing a glass keyboard.
Such pressure switch elements are known as touch panels in displays. The touch panels are normally made from transparent plastic films whose inner surfaces are coated with an electroconductive material. To support said films spacers are glued in the air gap, wherein a spacer arranged around the outside of the contact area is bonded in an airtight manner to the plastic films to stabilize the inside air pressure thus supporting the upper film. Inside the contact area elastic spacers are additionally provided which ensure return movement of the films. It is a drawback of the known pressure switch element that it requires a hermetically sealed air space which does not allow for any pressure compensation. In the event of considerable deviation from the normal atmospheric pressure, e.g. during application in submarine vehicles or in aeronautics and space operations, and at high temperatures hairline cracks occur in the vapour-deposited electroconductive contact layer due to the changes in air pressure, which results in a failure of the unit. At large heights the spacer in the contact area expands. This changes the switching path of the contact film, and the given electronical and mechanical parameters, such as the action point, are no longer complied with. Further drawbacks of the known touch panels are that the plastic films present only a limited mechanical and chemical resistance, a-small degree of transmission and are not antistatic. Further, in the event of temperature variation there is the danger of crack formation in the electroconductive layer due to fact that the expansion coefficients of the conductive layer and the plastic carrier considerably differ from each other.
From EP 0 546 003 B1 a pressure switch element made from a glass laminate is known which comprises a flexible thin glass pane and at least one carrier glass pane, each pane being provided with an electroconductive layer on the faces facing each other. The opposing electroconductive layers are kept at a distance to each other with the aid of a spacer. The electroconductive layers touch each other when pressure is applied to the flexible thin glass layer at the essentially localized place of pressure load application.
With regard to this type of pressure switch element it is common practice to provide the electrode connections of the electroconductive layers at a protruding edge of the carrier material pane.
For this purpose the electroconductive layer on the thin glass pane is bonded to the thicker carrier glass pane via an electroconductive spacer and then glued to a flexible multiple cable at the protruding edge. It is a drawback that microcracks occur due to the membrane effect of the thin glass pane when pressure is applied to the electroconductive spacer, which may lead to malfunction.
It is the object of the invention to provide a glass keyboard which can be produced at less expenditure and presents high contact reliability with regard to the electrical connections.
According to the invention the electroconductive layers on the thin glass pane and the carrier material pane are preferably connected with conductors which are led out at a side edge of the keyboard surface, that a flexible flat multiple cable is electrically connected with the conductors on the thin glass pane and the carrier material pane, and that the flat multiple cable is arranged between the thin glass pane and the carrier material pane.
In this way the conductors of the thin glass pane are bonded in a protected area within the glass keyboard with the flat multiple cable being insulatingly coated on the side averting the conductors.
The invention further provides a method for producing glass keyboards where a thin glass pane is glued at a distance to the carrier material pane with a flat multiple cable being connected,-simultaneously on two planes, in a contact-proof and break-proof manner with the electroconductive layers.
Preferably a first flat multiple cable is electroconductingly glued to the thin glass pane while a second flat multiple cable is electroconductingly glued to the carrier material pane. On each rear side the film-type flat multiple cable is insulated.
The thickness of the film-type flat multiple cable corresponds to the thickness of the spacer preferably made up of an adhesive arranged between the thin glass pane and the carrier material pane such that the flat multiple cables may preferably be inserted at a side edge of the glass keyboard so as to act as spacers.
The flat multiple cables are arranged at a lateral distance to each other between the thin glass pane and the carrier material pane. The gaps are filled with an adhesive, preferably a plastic material cured under UV-light.
Between the contacts connected with the conductors of a flat multiple cable, too, recesses may be left. Said recesses are also filled with an adhesive cured under UV-light. Due to the glueing in the recesses and the gaps mechanical pressure in this area of the thin glass pane does not lead to cracking of the glass since the adhesive serves as a spacer and further compensates for different film material thicknesses of the flat multiple cables.
The flat multiple cables are connected at their free ends with a multiple plug connector. A microprocessor may be integrated in the flat multiple cables or in the multiple plug connector.
According to a preferred aspect the carrier material pane is slightly larger than the flexible thin glass pane such that the marginal area of the carrier material pane protrudes beyond the the marginal area of the thin glass pane. The protruding marginal area of the carrier material pane protects the sensitive marginal edge of the thin glass pane, which can further reduce the danger of breakage of the thin glass pane.
The the flat set back margin of the thin glass pane is glued to the marginal area of the carrier material pane by means of an adhesive acting as a spacer in the marginal area. The protruding margin of the carrier material pane is further adapted to receive an adhesive build-up which also protects the sensitive edge of the thin glass pane.
Preferably the margin of the thin glass pane is stabilized by means of a cured plastic material. The cutting edge of the thin glass pane displays a plurality of microcracks which occur during the cutting process and extend from the edge to the inside. Said microcracks may easily result in a crack which destroys the entire thin glass pane. The margin of the thin glass pane is therefore preferably stabilized by means of a cured plastic material. For this purpose the boundary edges of the thin glass pane are dipped into a liquid plastic material. Due to the capillary effect the microcracks are filled with the liquid plastic material whereafter the plastic material cures. When the plastic material is cured, the thin glass pane offers a considerably higher stability since breaking of the thin glass pane starting from its margins can no longer occur in the event of pressure or shock load.
The thickness of the thin glass pane ranges between approximately 0.1 and 0.5 mm, preferably between approximately 0.175 and 0.4 mm. A thin glass pane of such a thickness offers an adequate flexibility to allow for localized switching contact between opposing electroconductive layers.
The spacer is arranged exclusively in the marginal area of the keyboard surface between the thin glass pane and the carrier material pane, wherein in the remaining portion of the keyboard surface switching operations can be performed formed at any location without further spacers being provided. The invention preferably makes additional spacers in the area of the switching section superfluous such that the overall keyboard surface is available for switching operations without any limitations.
In a preferred embodiment the spacer in the marginal area is made from a plastic material cured under UV-light. This offers the advantage that no separate spacer has to be provided, and that the spacer can already be formed when the thin glass pane is glued to the carrier material pane.
The carrier material pane and/or the spacer comprise in the marginal area vent openings for the space between the thin glass pane and the carrier material pane. This offers the advantage that pressure compensation is possible in the event of deviation from the normal atmospheric pressure, e.g. during application in submarine vehicles or in aeronautics and space operations, and at high temperatures such that the electroconductive layers on the thin glass pane and the carrier material pane are prevented from being damaged.
The vent openings are preferably provided with a filter material protecting the glass keyboard from soiling.
Further preferred features of the invention are stated in the subclaims.
Hereunder embodiments of the invention are explained in detail with reference to the drawings in which: